US9859089B2 - Method and system for inspecting and grounding an EUV mask - Google Patents
Method and system for inspecting and grounding an EUV mask Download PDFInfo
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- US9859089B2 US9859089B2 US14/796,565 US201514796565A US9859089B2 US 9859089 B2 US9859089 B2 US 9859089B2 US 201514796565 A US201514796565 A US 201514796565A US 9859089 B2 US9859089 B2 US 9859089B2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/026—Means for avoiding or neutralising unwanted electrical charges on tube components
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/20—Means for supporting or positioning the objects or the material; Means for adjusting diaphragms or lenses associated with the support
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/004—Charge control of objects or beams
- H01J2237/0041—Neutralising arrangements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/004—Charge control of objects or beams
- H01J2237/0041—Neutralising arrangements
- H01J2237/0044—Neutralising arrangements of objects being observed or treated
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/20—Positioning, supporting, modifying or maintaining the physical state of objects being observed or treated
- H01J2237/2008—Positioning, supporting, modifying or maintaining the physical state of objects being observed or treated specially adapted for studying electrical or magnetical properties of objects
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/26—Electron or ion microscopes
- H01J2237/28—Scanning microscopes
- H01J2237/2809—Scanning microscopes characterised by the imaging problems involved
- H01J2237/2811—Large objects
Definitions
- the present invention relates to a system for inspecting an EUV mask by using a charged particle beam, and more especially, to a system for grounding an EUV mask when the EUV mask is inspected by using a charged particle beam.
- Optical inspection of a mask is based on a comparison of the light signals in the patterned regions relative to the non-patterned regions.
- a high contrast is necessary in order to achieve sufficient sensitivity for defect detection.
- the transmissive masks used in DUV (deep Ultra Violet) lithography can be inspected without difficulty since the contrast between the opaque regions and the clear regions is high at UV/DUV wavelengths.
- the EUV mask for example used in EUV lithography since not only the contrast between the absorber region and the mirror region is low at UV/DUV wavelengths, but also wavelength of the UV/DUV is too lengthy to inspect EUV mask.
- Optical inspection of a mask is based on a comparison of the light signals in the patterned regions relative to the non-patterned regions.
- a high contrast is necessary in order to achieve sufficient sensitivity for defect detection.
- the transmissive masks used in DUV (deep Ultra Violet) lithography can be inspected without difficulty since the contrast between the opaque regions and the clear regions is high at UV/DUV wavelengths.
- the EUV mask for example used in EUV lithography since not only the contrast between the absorber region and the mirror region is low at UV/DUV wavelengths, but also wavelength of the UV/DUV is too lengthy to inspect EUV mask.
- an electron beam (E-beam) inspection tool accordingly, is developed to inspect the EUV mask.
- E-beam electron beam
- accumulated charging on EUV mask will induce inspection issue while the EUV mask is inspected by the E-beam inspection tool. This issue will not happen to silicon wafer because silicon wafer can be grounded.
- Substrate of the EUV mask is dielectric, and cannot be grounded.
- the contrast and intensity of the scanned images at different areas would not be consistent or equal during the inspection process.
- the electron beam scanning over different regions of the EUV mask would cause dwell times in order to make the images have better quality and consistent contrast and intensity during the inspection operation.
- the inspection speed and the throughput would be influenced greatly.
- one object of this invention is to provide a structure to discharge the EUV mask during inspection by an E-beam inspection tool, so that non accumulated charging is on the EUV mask during E-beam inspecting to enhance the inspection quality.
- one embodiment of the present invention provides a structure for discharging EUV mask including: means for conducting charge on an EUV mask in inspecting the EUV mask by using a charged particle beam inspection system; and a grounding pin to contact the means.
- Another embodiment of the present invention provides a structure for discharging EUV mask including: at least a conductive layer on one side of an EUV mask; and a grounding pin to contact the conductive layer, so that charge on a reflective surface of the EUV mask is grounded through the conductive layer to the grounding pin.
- Another embodiment of the present invention provides a structure for discharging EUV mask including: a first conductive layer on one side of an EUV mask; a second conductive layer on a surface opposite to a reflective surface of the EUV mask; and a grounding pin to contact the second conductive layer, so that charge on the reflective surface of the EUV mask is grounded through the second conductive layer to the grounding pin.
- an electron beam inspection system for inspecting an EUV mask including: an electron gun for providing electron beam; a lens for focusing the electron beam on the EUV mask; a detector for receiving signal electron emanating from the EUV mask; and means for discharging the EUV mask during the EUV mask is inspected.
- Another embodiment of the present invention provides a method for inspecting an EUV mask by using a charged particle beam including: grounding the EUV mask; moving a stage, for supporting the EUV mask, continuously and scanning a surface of the EUV mask by using the charged particle beam simultaneously; and receiving signal electrons emanated from the surface of the EUV mask.
- Another embodiment of the present invention provides a system for inspecting an EUV mask including: a source for providing an electron beam; an objective lens for focusing the electron beam on a surface of the EUV mask; a detector for receiving signal electrons emanated from the surface of the EUV mask; a stage for supporting the EUV mask; and means for grounding the EUV mask, wherein the surface of the EUV mask is scanned by the electron beam when the stage moves continuously,
- Another embodiment of the present invention provides a method for inspecting an EUV mask by using a charged particle beam, which comprises steps of grounding the EUV mask, moving a stage continuously and scanning a reflective surface of the EUV mask by using the charged particle beam simultaneously, and receiving signal electrons emanated from the surface of the EUV mask, wherein the stage supports the EUV mask.
- the charged particle beam can be an electron beam.
- a stage's moving direction is perpendicular to a scanning direction of the electron beam.
- the EUV mask can be inspected by a low voltage scanning electron microscope.
- the step of grounding the EUV mask can be performed by slightly contacting a grounding pin to the reflective surface of the EUV mask.
- the step of grounding the EUV mask can be performed by contacting a grounding pin to a back surface of the EUV mask and electrically connecting to the reflective surface of the EUV mask.
- the grounding pin can contact the back surface of the EUV mask slightly.
- the step of grounding the EUV mask can be performed by slightly contacting a grounding pin to a conductive layer on one side wall of the EUV mask.
- a trench can be formed in the side wall of the EUV mask.
- the conductive layer can be coated within the trench.
- Another embodiment of the present invention provides a system for inspecting an EUV mask, which comprises a source for providing an electron beam, an objective lens for focusing the electron beam on a reflective surface of the EUV mask, a detector for receiving signal electrons emanated from the surface of the EUV mask, a stage for supporting the EUV mask, and means for grounding the EUV mask, wherein the surface of the EUV mask is scanned by the electron beam when the stage moves continuously.
- a stage's moving direction is perpendicular to a scanning direction of the electron beam.
- the system can be a low voltage scanning electron microscope.
- the means for grounding the EUV mask can include a grounding pin slightly contacting the reflective surface of the EUV mask.
- the means for grounding the EUV mask can include a grounding pin contacting a back surface of the EUV mask, and a conductive layer can be on the back surface of the EUV mask and electrically connecting to the reflective surface of the EUV mask.
- the grounding pin can contact the back surface of the EUV mask slightly.
- the means for grounding the EUV mask can include a grounding pin contacting a conductive layer on one side wall of the EUV mask.
- a trench can be formed in the side wall of the EUV mask.
- the conductive layer can be coated within the trench.
- This invention also provides a system for grounding an EUV mask when the EUV mask is inspected by using a charged particle beam.
- the system comprises means for conducting charges from a reflective surface of the EUV mask, and means for grounding the charges by directly contacting said conducting means.
- the conducting means is mounted on the EUV mask such that the charges induced by the charged particle beam can be grounded.
- the conducting means can be an electrically conductive cap for mounting on a corner of the EUV mask, an electrically conductive wire for mounting on peripheral regions of the reflective surface, or a hollow, electrically conductive cover for mounting on peripheral regions of the reflective surface.
- the grounding means can include a base and at least an electrically conductive wire protruding from the base.
- the grounding means can include a base, one fork mounting on the base, and an electrically conductive wire between the two ends of said fork.
- FIG. 1 illustrates a cross-sectional view of a configuration of an EUV mask
- FIG. 2 illustrates a vertical view of a configuration of an EUV mask
- FIG. 3 a and FIG. 3 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the first embodiment of the present invention
- FIG. 4 illustrates a diagram about a configuration of the EUV mask and the slider
- FIG. 5 illustrates a diagram about a configuration of the EUV mask and the electron gun
- FIG. 6 a and FIG. 6 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the second embodiment of the present invention
- FIG. 7 a and FIG. 7 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the third embodiment of the present invention
- FIG. 8 illustrates a first embodiment of the grounding pin controlling structure
- FIG. 9 a , FIG. 9 b and FIG. 9 c illustrates a second embodiment of the grounding pin controlling structure
- FIG. 10 a , FIG. 10 b and FIG. 10 c illustrates a third embodiment of the grounding pin controlling structure
- FIG. 11 illustrates a cross-sectional view of a configuration of another EUV mask
- FIG. 12 a and FIG. 12 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the fourth embodiment of the present invention
- FIG. 13 a and FIG. 13 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the fifth embodiment of the present invention
- FIG. 14 illustrates the diagrams about the working status of the EUV mask and the grounding pin in accordance with the sixth embodiment of the present invention
- FIG. 15 a and FIG. 15 b respectively illustrates a cross-sectional view and a vertical view of a configuration of another EUV mask
- FIG. 16 illustrates a diagram of a conductive holder clamping the EUV mask in accordance with another embodiment of the present invention.
- FIG. 17 illustrates a vertical view of a configuration of another EUV mask
- FIG. 18 illustrates a vertical view of a configuration of another EUV mask.
- FIG. 19 is a flow chart illustrating a method for inspecting an EUV mask by using a charged particle beam in accordance with one embodiment of the present invention.
- FIG. 20 shows an embodiment of a low voltage scanning electron microscope.
- FIG. 21 shows a schematic diagram of a structure for an electron beam inspection system processing continuous scanning on an EUV mask in accordance with one embodiment of the present invention.
- FIG. 22 a and FIG. 22 b show a schematic diagram of a structure for an electrically conductive cap which mounts on a corner of an EUV mask in accordance with one embodiment of the present invention.
- FIG. 23 a and FIG. 23 b show a schematic diagram of a structure for an electrically conductive wire which mounts on peripheral regions of an EUV mask in accordance with one embodiment of the present invention.
- FIG. 24 a and FIG. 24 b show a schematic diagram of a structure for a hollow, electrically conductive cover which mounts on peripheral regions of an EUV mask in accordance with one embodiment of the present invention.
- FIG. 25 a , FIG. 25 b and FIG. 25 c show a schematic diagram of a structure for grounding charges on an EUV mask in accordance with one embodiment of the present invention.
- FIG. 26 a and FIG. 26 b show a schematic diagram of a structure for grounding charges on an EUV mask in accordance with another embodiment of the present invention.
- FIG. 27 show a schematic diagram of the structure in FIG. 25 c for grounding charges on an EUV mask in accordance with one embodiment of the present invention.
- FIG. 28 show a schematic diagram of the structure in FIG. 26 b for grounding charges on an EUV mask in accordance with one embodiment of the present invention.
- FIG. 1 illustrates a cross-sectional view of a configuration of an EUV mask.
- the EUV mask 10 includes a substrate 12 , an EUV absorption layer 14 on the substrate 12 and a patterned reflective surface 16 formed on the absorption layer 14 .
- the patterned reflective surface 16 has a peripheral area 161 without any pattern and a middle area 162 with a plurality of pattern openings 163 thereon.
- the patterned reflective surface of the EUV mask may be holes, circuits, devices, or any combination thereof.
- the reflective layer made of the same or different metals, is formed on a substrate of the EUV mask, and portion of the plurality of patterns may distribute on the reflective layer.
- a structure for discharging EUV mask includes: means for conducting charge on the EUV mask 10 in inspecting the EUV mask 10 by using a charged particle beam inspection system; and a grounding pin (shown in following diagrams) to contact the means.
- the grounding pin is used to contact a portion of the peripheral area 161 of the patterned reflective surface 16 , which is made of electrical conductive materials, or electrical semiconductive materials, and thereby grounds charges on the reflective surface 16 of the EUV mask 10 .
- FIG. 3 a and FIG. 3 b illustrate the diagrams about the working of the EUV mask and the grounding pin in accordance with the first embodiment of the present invention.
- the structure 20 for discharging EUV mask further includes a slider 22 , a spring 24 and an arm structure 26 .
- the slider 22 has a top surface 28 divided into a flat area 281 and a downward-tilted area 282 .
- One end of the spring 24 connects to a back side 221 of the slider 22 and the other end of the spring 24 is fixed.
- the arm structure 26 is above the slider 22 and the arm structure 26 includes a body 261 , the grounding pin 262 on a front end of the body 261 and a prop 263 connecting to the body 261 . As shown in FIG.
- the slider 22 has a gap 30 on the front side 222 of the slider 22 for holding one corner of the EUV mask 10 , so that the slider 22 may fix the EUV mask 10 , as the EUV mask 10 contacts with the slider 22 during the EUV mask 10 is grounded by the grounding pin 262 (shown in FIG. 3 a , FIG. 3 b ) and inspected by charged particle beam inspection system, in which the electron gun 32 for providing electron beam is above the EUV mask 10 , as shown in FIG. 5 .
- FIG. 6 a and FIG. 6 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the second embodiment of the present invention.
- the structure 40 for discharging EUV mask further includes a gripper unit 42 , an arm structure 44 , a reciprocating member 46 and two resilient members 48 , 48 ′.
- the gripper unit 42 includes a head portion 421 , a base portion 422 and a first rolling member 423 set at a bottom end of the base portion 421 .
- the gripper unit 42 is used for fixing the EUV mask 10 in place, for example but not limited to, being held tight or to be released, through rotation of the gripper unit 42 about a first pivot 424 substantially parallel with a first center axis of the first rolling member 423 .
- the arm structure 44 is configured near or opposite the gripper unit 42 .
- the arm structure 44 includes a body 441 , the grounding pin 50 on a top end of the body 441 and a second rolling member 442 set at a bottom end of the body 441 .
- the grounding pin 50 may reciprocate to contact the EUV mask 10 and leave the EUV mask 10 through rotation of the body 441 about a second pivot 443 substantially parallel with a second center axis of the second rolling member 442 .
- the two resilient members are one first resilient member 48 and one second resilient member 48 ′ each with one end being fixed, and respectively with the other ends being connected to head portion 422 of the gripper unit 42 and to the body 441 of the arm structure 44 for respectively providing a first force to the gripper unit 42 toward a first direction 52 and a second force to the body 441 of the arm structure 44 toward a second direction 54 .
- the reciprocating member 46 is configured for causing the first rolling member 423 and the second rolling member 442 to rotate.
- the reciprocating member 46 includes a fix end 461 and a mobile end 462 pivoting the fixed end 461 .
- the first rolling member 423 and the second rolling member 442 may be in contact with reciprocating member 46 and roll freely on the surface of the reciprocating member 46 .
- the reciprocating member 46 is tilted by pushing up and pulling down the mobile end 462 of the reciprocating member 46 pivoting the fixed end 461 of the reciprocating member 46 , which results in the first rolling member 423 and the second rolling member 442 rolling on the reciprocating member 46 .
- the head portion 422 of the gripper unit 42 moves toward the first direction 52 by means of the first force of the first resilient member 48 and an upper portion of the arm structure 44 moves toward the second direction 54 by means of the second force of the second resilient member 48 ′, so that the head portion 422 is therefore led toward the edge of the EUV mask 10 and in the end to abut against the EUV mask 10 , and the grounding pin 50 contacts the reflective surface 16 of the EUV mask 10 .
- the head portion 422 of the gripper unit 42 is used to push tighter against the EUV mask 10 to hold it fixed in position during the EUV mask 10 is grounded by the grounding pin 50 and inspected by the charged particle beam inspection system.
- FIG. 7 a and FIG. 7 b illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the third embodiment of the present invention.
- the structure for discharging EUV mask further includes the foregoing gripper unit 42 , the foregoing first resilient member 48 , the foregoing reciprocating member 46 and a grounding pin controlling structure 60 .
- the structures, the connection relations and the operation of the gripper unit 42 , the first resilient member 48 and the reciprocating member 46 are described in the second embodiment as shown in FIG. 6 a and FIG.
- the grounding pin controlling structure 60 includes a hollow cylinder 62 and a column 64 passing through the hollow cylinder 62 .
- a grounding pin 50 is arranged on a top surface of the column 64 and the position of the grounding pin 50 is changed by moving the column 64 .
- FIG. 7 a when the gripper unit 42 pushes tighter against the EUV mask 10 , the column 64 moves down and the grounding pin 50 contacts the reflective surface 16 of the EUV mask 10 .
- FIG. 7 b when the gripper unit 42 releases the EUV mask 10 , the column 62 moves up and the grounding pin 50 is far away from the EUV mask 10 .
- the grounding pin controlling structure 60 includes a hollow cylinder 62 and a column 64 passing through the hollow cylinder 62 , wherein the column 64 has an interior room 641 , as shown in FIG. 8 .
- a first rod 66 with the spiral shells 661 on the outer surface and a second rod 68 with the sawtooth 681 on the outer surface are configured in the interior room 641 , wherein the spiral shells 661 and the sawtooth 681 are engaged with each other.
- a first pushing shaft 70 is connected to the bottom of the column 64 and a second pushing shaft 72 is connected to the bottom of the second rod 68 and passes through the bottom of the column 64 .
- connection rod 74 is connected to the top of the first rod 66 , and another end of the connection rod 74 is connected with a grounding pin 50 .
- the column 64 moves down in relative to the hollow cylinder 62 (shown in FIG. 7 a ), so that the grounding pin 50 contacts the reflective surface 16 of the EUV mask 10 (shown in FIG. 7 a ).
- the column 64 moves up continuously in relative to the hollow cylinder 62 (shown in FIG.
- the grounding pin controlling structure 60 includes a hollow cylinder 62 and a column 64 passing through the hollow cylinder 62 .
- the hollow cylinder 62 has two opposite trenches 80 formed on an inner surface 621 of a side wall 622 of the hollow cylinder 62 , wherein each trench 80 has a lengthwise ditch 801 and an upward-tilted ditch 802 connecting to a top end of the lengthwise ditch 801 .
- each trench 80 has a lengthwise ditch 801 and an upward-tilted ditch 802 connecting to a top end of the lengthwise ditch 801 .
- the column 64 has two opposite protrusions 82 on an outer surface of the column 64 and the protrusions 82 are respectively arranged within the opposite trenches 80 , as shown in FIG. 9 a to move along the lengthwise ditch 801 and the upward-tilted ditch 802 .
- the column 64 moves down in relative to the hollow cylinder 62 (shown in FIG. 7 a ), so that the grounding pin 50 contacts the reflective surface 16 of the EUV mask 10 (shown in FIG. 7 a ).
- the column 64 moves up continuously in relative to the hollow cylinder 62 , wherein the column 64 moves up straightly and then deflects as protrusions 82 moves along the lengthwise ditch 801 and then the upward-tilted ditch 802 , so that the grounding pin 50 is far away from the EUV mask 10 .
- the grounding pin controlling structure 60 includes a hollow cylinder 62 and a column 64 passing through the hollow cylinder 62 .
- the hollow cylinder 62 has two opposite trenches 84 passing through a side wall 622 of the hollow cylinder 62 , wherein each trench 84 has a lengthwise ditch 841 passing through the side wall 622 and a upward-tilted ditch 842 passing through the side wall 622 and connecting to a top end of the lengthwise ditch 841 .
- FIG. 10 a the grounding pin controlling structure 60 includes a hollow cylinder 62 and a column 64 passing through the hollow cylinder 62 .
- the hollow cylinder 62 has two opposite trenches 84 passing through a side wall 622 of the hollow cylinder 62 , wherein each trench 84 has a lengthwise ditch 841 passing through the side wall 622 and a upward-tilted ditch 842 passing through the side wall 622 and connecting to a top end of the lengthwise ditch 841 .
- FIG. 10 a the grounding pin
- the column 64 has two opposite branch structures 86 including at least two horizontal rods 861 respectively, and the branch structures 86 are respectively arranged within the opposite trenches 84 , as shown in FIG. 10 a , to move along the lengthwise ditch 841 and the upward-tilted ditch 842 .
- the column 64 moves down in relative to the hollow cylinder 62 (shown in FIG. 7 a ), so that the grounding pin 50 contacts the reflective surface 16 of the EUV mask 10 (shown in FIG. 7 a ).
- the column 64 moves up continuously in relative to the hollow cylinder 62 , wherein the column 64 moves up straightly and then deflects as the branch structures 86 moves along the lengthwise ditch 841 and the upward-tilted ditch 842 , so that the grounding pin 50 is far away the EUV mask 10 .
- the grounding pin 50 is used to contact the reflective surface 16 which is formed on the top surface of the EUV mask 10 . Nevertheless, the position that the grounding pin contacts with may be changed. As shown in FIG. 11 , a first conductive layer 90 and a second conductive layer 92 may respectively be coated on the side of the EUV mask 10 and coated on the bottom surface, which is opposed to the reflective layer 16 , of the EUV mask 10 .
- the reflective surface 16 , the first conductive layer 90 and the second conductive layer 92 are electrically connected, so that the foregoing grounding pin 50 may be used to contact the second conductive layer 92 , so that charge on the reflective surface 16 of the EUV 10 mask is grounded through the first conductive layer 90 and the second conductive layer 92 to the grounding pin 50 .
- the coated first conductive layer 90 and the second conductive layer 92 may be Al, Cr, Ti, alloy thereof, or non-metal such as carbon.
- the thickness of the first conductive layer 90 and the second conductive layer 92 may be 0.001 um to 1 mm.
- the drive mechanism of the gripper unit described in the second embodiment of the present invention may be applied to the EUV mask with the first conductive layer and the second conductive layer.
- the reciprocating member 46 works to make the third rolling member 94 to move substantially along the third direction 98 and the fourth rolling member 96 move substantially along the fourth direction 100
- the head portion 422 of the gripper unit 42 moves toward the opposite direction of the third direction 98
- the grounding pin 50 moves toward the opposite direction of the fourth direction 100 so that the head portion 422 and the grounding pin 50 are led away from the EUV mask 10 .
- FIG. 12 a when the reciprocating member 46 works to make the third rolling member 94 to move substantially along the third direction 98 and the fourth rolling member 96 move substantially along the fourth direction 100 , the head portion 422 of the gripper unit 42 moves toward the opposite direction of the third direction 98 and the grounding pin 50 moves toward the opposite direction of the fourth direction 100 so that the head portion 422 and the grounding pin 50 are led away from the EUV mask 10 .
- the head portion 422 of the gripper unit 42 moves toward the third direction 98 by means of the third force of the third resilient member 102 and an upper portion of the arm structure 44 moves toward the fourth direction 100 by means of the fourth force of the fourth resilient member 102 ′ so that the head portion 422 is therefore led toward the edge of the EUV mask 10 and in the end to abut against the EUV mask 10 , and the grounding pin 50 contacts the second conductive layer 92 of the EUV mask 10 to discharge the charge on the reflective surface 16 of the EUV mask 10 .
- the grounding pin controlling structure 60 described in third embodiment of the present invention may also be applied to the EUV mask 10 with the first conductive layer 90 and the second conductive layer 92 thereon.
- the column 64 moves up and the grounding pin 50 contacts the second conductive layer 92 of the EUV mask 10 .
- the column 64 moves down and the grounding pin 50 is far away from the EUV mask 10 .
- the embodiments of the grounding pin controlling structure 60 are described above, and unnecessary details would not be given here.
- the grounding pin may be a spring 110 with a trigger 112 on the top end of the spring 110 , and the bottom end of the spring 110 is grounded.
- the second conductive layer 92 of the EUV mask 10 may contact with the trigger 112 by the weight of the EUV mask 10 to discharge the charge on the reflective surface 16 of the EUV mask 10 .
- the grounding pin is used to contact at least one conductive layer on one side of the EUV mask.
- a conductive layer 93 is formed on one corner of the EUV mask 10 , the two adjacent side walls 105 , 105 ′, accordingly, and the conductive layer 93 is electrically connected to the reflective surface 16 of the EUV mask 10 .
- the structure for discharging EUV mask includes a conductive holder 130 with the grounding pin 50 , as shown in FIG. 16 , to clamp the corner of the EUV mask 10 , so that the grounding pin 50 may contact with the conductive layer 93 . Refer to FIG.
- two grounding pins 50 are respectively formed on a pair of opposite clamp sections 131 of the conductive holder 130 , so that the two grounding pins 50 may contact the conductive layer 13 at two adjacent side walls 105 , 105 ′ of the EUV mask 10 .
- two trenches 132 or notches are respectively formed on two adjacent side walls 105 , 105 ′ of the EUV mask 10 , and a conductive layer 93 formed on the trenches 132 or the notches is electrically connected to the reflective surface 16 of the EUV mask 10 .
- the profile of the trenches 132 or notches may correspond to the grounding pins 50 arranged on the conductive holder 130 as shown in FIG. 16 , so that the grounding pin 50 may closely contact the conductive layer 93 .
- the foregoing conductive layer 93 may be formed on the whole side wall, including the trenches 132 or the notches walls, of the EUV mask 10 , so that the grounding pin 50 may contact with the conductive layer 93 conveniently.
- the coated conductive layer 93 may be Al, Cr, Ti, alloy thereof, or non-metal such as carbon.
- the thickness of the conductive layer 93 may be 0.001 um to 1 mm.
- FIG. 19 is a flow chart illustrating a method for inspecting an EUV mask by using a charged particle beam according to an embodiment of the present invention.
- a grounding pin slightly contacts to the EUV mask while the EUV mask is positioned.
- the grounding pin can contact the reflective surface, backside surface, or sidewall surface of the EUV mask to achieve a discharging effect.
- a stage, for supporting the EUV mask is moved continuously, and the reflective surface of the EUV mask is scanned by using a charged particle beam simultaneously. Furthermore, the moving direction of the stage is perpendicular to the scanning direction of the charged particle beam.
- the charged particle beam in one embodiment, is electron beam.
- signal electrons emanated from the reflective surface of the EUV mask can be received by a detector to form an imaging.
- the signal electrons can be secondary electrons or backscattered electrons.
- FIG. 20 shows a low voltage scanning electron microscope (LVSEM) used to inspect a EUV mask.
- an objective lens can be a SORIL optical system.
- the electron beam 304 emitted from a cathode 302 is accelerated by an anode 306 voltage, passes through a gun aperture 308 , a condenser lens 310 , a beam limit aperture 312 and a SORIL system 316 , and then impinges onto a specimen surface 326 supported by a stage 328 .
- the electron beam 304 is emanated from the cathode 302 along an optical axis.
- the emanated electrons are firstly accelerated in the space between the cathode 302 and anode 306 , and then decelerated (accelerated or remain even speed in some cases) in the space between the anode 306 and a terminal electrode at ground potential.
- the electron beam 304 with larger polar angles can be cut off by the gun aperture 306 , and trimmed down to a specific current value. It can also be earlier to prevent from the Coulomb interaction of the electron beam. Then the electron beam 304 passes the condenser lens 310 and the beam limit aperture 312 .
- the condenser lens 310 can weakly condense the electron beam 304 .
- the beam limit aperture 312 can determine the amount of the electron beam 304 to a desired beam current on the specimen 326 , and allow entering the objective lens system 316 with a fixed energy, a fixed brightness and a fixed beam current.
- the SORIL system 316 includes an objective lens 318 , deflectors 320 and 322 which are located inside the objective lens 318 , and a control electrode 324 .
- the objective lens 318 can be an immersion electrostatic objective lens, an immersion magnetic objective lens, or an electromagnetic compound objective lens. In the embodiment, the immersion magnetic objective lens 318 is more preferred.
- the immersion magnetic objective lens 318 can focus the electron beam 304 into a small spot which is used to scan the studied specimen 326 . Because focusing the electron beam 304 is mainly accomplished by the magnetic objective lens 318 , the aberrations of the beam spot mostly come from the spherical aberration and the chromatic aberration of the magnetic objective lens 318 .
- the purpose of the immersion magnetic objective lens 318 is to generate a magnetic field with a large component perpendicular to the Z-axis for converging lens action above the specimen 326 and to have the magnetic field substantially parallel to the Z-axis at the specimen 326 . Accordingly, the specimen 326 can be immersed in the magnetic field of the lens.
- the deflection units 320 and 322 in the SORIL system 316 can be equipped with electrostatic multi-pole deflectors or magnetic multi-pole deflectors.
- the embodiment is more preferred the electrostatic multi-pole deflectors because the magnetic multi-pole deflectors would produce magnetic hysteresis phenomenon on deflecting the electron beam 304 during operation. Therefore, it would affect the scanning speed.
- the electron beam 304 can be deflected by the deflection units 320 and 322 which can generate a small deflection field, or can work together with the control electrode 324 to increase the size of the deflection field, so that the specimen 326 can be scanned by the focused beam.
- the deflection units are designed to minimize the introduction of aberrations into the beam when deflecting the electron beam.
- the deflection units 320 and 322 are dedicated to produce a more rapid scanning movement of the electron beam 304 to cover a suspected region, and it can enhance the throughput of the imaging.
- the control electrode 324 is made of electrical conduction material.
- the control electrode 324 is shaped and positioned to be an extension of outer polepiece of the magnetic objective lens 318 towards optical axis.
- the control electrode 324 is set to a voltage Vce to control the electrical field on the specimen surface 326 lower than the predetermined value, which ensures on micro-arcing on the specimen surface 326 .
- the voltage Vce of the control electrode 324 can be dynamically adjusted to compensate the image defocus due to electric drifting.
- the control electrode 324 can be dynamically performing micro-focusing while the image is defocused.
- the control electrode 324 can increase the magnetic field strength of the SORIL system 316 under a same excitation.
- control electrode 324 Placing the control electrode 324 in the retarding field gives the control electrode 324 a great deal of influence over the trajectory of the electron beam 304 because the electron beam 304 has been reduced to a lower landing energy than the deflection units 320 and 322 , and it is nearest the landing point of the electron beam on the specimen 326 . Furthermore, because of its proximity to the specimen 326 , it can help to accurately position the electron beam 304 over a selected area of the specimen 326 prior to the rapid scan of the area, and improve the size of the deflection field over the specimen 326 .
- the SORIL system 316 adopted in the embodiment is preferred because it can reduce the off-axis chromatic and spherical aberrations greatly in scanning imaging, and is better at extending its magnetic field below the lens aperture and through the specimen 326 to increase the field of view.
- the embodiment of the present invention can adopt the multi-channel detector 314 to collect the signal electrons during the scanning operation.
- the signal electrons, including the secondary electrons or the backscattered electrons, emanated from the different sides or features of the specimen surface 326 can be collected by different channels. Therefore, the signal electrons from the different emanated directions can generate a stereo image in combination, and finally ensure a topography analysis of the defects of interest regions.
- the specimen 326 on the specimen stage 328 is charged with a negative voltage to create a retarding field Er; that is, a field in the opposite direction to the accelerating field Ea to reduce the energy of the electron beam prior to impact with the specimen 326 , and avoid great damage of the specimen surface. Furthermore, the retarding field can make the electron beam 304 land on the specimen surface with a lower landing energy.
- FIG. 21 shows a schematic diagram of a structure 500 for an electron beam inspection system processing continuous scanning on a EUV mask.
- the electron beam inspection system adopts the LVSEM disclosed in the FIG. 20 , and is expressed in a simplified manner.
- a stage 522 on the inspecting system is used for supporting the EUV mask 520 .
- the reflective surface of the EUV mask 520 is continuously scanned by using the electron beam 504 when the stage 522 moves continuously at the same time.
- the stage 522 can move along the direction 526 and the surface of EUV mask 520 can be scanned by the electron beam 504 under the control of the first deflector 514 and the second deflector 516 .
- the moving direction of the stage is perpendicular to the scanning direction of the electron beam.
- the present invention provides a structure to discharge the EUV mask during inspection by an E-beam inspection tool, so that non accumulated charging is on the EUV mask during E-beam inspecting to enhance the inspection quality.
- the electron beam inspection system for inspecting an EUV mask includes: an electron gun for providing electron beam; a lens for focusing the electron beam on the EUV mask; a detector for receiving signal electrons emanating from the EUV mask; and means for discharging the EUV mask during the EUV mask is inspected; the reflective surface of the EUV mask on a continuous moving stage is scanned by using the electron beam simultaneously under the control of the first deflector and second deflector; the movement direction of the stage is perpendicular to the scanning direction of the electron beam.
- the inspection quality of the EUV mask is enhanced by using the electron beam inspection system because the accumulated charging on the EUV mask is grounded.
- this invention provides means for conducting charges from the reflective surface of the EUV mask, such that any tiny scratch on the reflective surface of the EUV mask can be avoided.
- the grounding pin then directly contacts the conducting means to ground charges on the reflective surface.
- Variant conducting means can be referred to FIG. 22 to FIG. 24 .
- an electrically conductive cap 1610 is provided for mounting on a corner of the EUV mask 10 . Because the reflective surface of the EUV mask 10 electrical conducts to the cap 1610 , charges on the reflective surface can be grounded via the cap 1610 . This embodiment provides a good protection for the EUV mask in grounding.
- One similar means which can be referred to FIG. 23 a and FIG. 23 b , is to use an electrically conductive wire 1620 for mounting on peripheral regions of the EUV mask 10 . To be more specific, only four corners on the reflective surface of the EUV mask are mounting be the wire 1620 , in order to reduce any possible contact between the reflect surface of the EUV mask and the wire 1620 .
- FIG. 24 a and FIG. 24 b Still another means, which can be referred to FIG. 24 . a and FIG. 24 b , is to use a hollow, electrically conductive cover for mounting on peripheral regions of the EUV mask.
- the embodiments in both FIG. 23 and FIG. 24 provide grounding in four directions and the latter provides a larger area for grounding pin, which in theoretical will provide better grounding efficiency.
- FIG. 25 a Still some grounding means 701 is provided in FIG. 25 a , in which a base 710 is provided with an electrically conductive wire 721 protruding from the base 710 .
- two electrically conductive wires 723 can be provided in FIG. 25 b as another grounding means 701 .
- the electrically conductive wire 725 in FIG. 25 c , can be a loop to form still another grounding means 703 .
- the single grounding wire 721 , two grounding wires 723 , or loop grounding wire 725 in the FIG. 25 respectively are used to contact the conducting means in the FIG. 22 to FIG. 24 and illustrated as top views.
- FIG. 26 a Another kind of grounding means 750 , in FIG. 26 a , includes a fork 760 on a base (not shown in FIG. 26 but similar to FIG. 25 ) and an electrically conductive wire 761 between the two ends of the fork 760 .
- an electrically conductive band 763 in FIG. 26 b is provided to form another grounding means 752 . Both the wire 761 and band 763 are used to contact the conducting means the FIG. 22 to FIG. 24 and illustrated as top views.
- the grounding means 703 is used to contact the EUV mask 10 , wherein any conducting means in FIG. 22 to FIG. 24 can also be applied to the EUV mask 10 .
- the grounding means 751 is used to contact the EUV mask 10 , wherein any conducting means in FIG. 22 to FIG. 24 can also be applied to the EUV mask 10 .
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Abstract
Description
Claims (7)
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US14/796,565 US9859089B2 (en) | 2011-05-20 | 2015-07-10 | Method and system for inspecting and grounding an EUV mask |
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US13/112,536 US8575573B2 (en) | 2011-05-20 | 2011-05-20 | Structure for discharging extreme ultraviolet mask |
US14/039,939 US9113538B2 (en) | 2011-05-20 | 2013-09-27 | Structure electron beam inspection system for inspecting extreme ultraviolet mask and structure for discharging extreme ultraviolet mask |
US14/575,102 US9485846B2 (en) | 2011-05-20 | 2014-12-18 | Method and system for inspecting an EUV mask |
US14/796,565 US9859089B2 (en) | 2011-05-20 | 2015-07-10 | Method and system for inspecting and grounding an EUV mask |
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US14/039,939 Continuation-In-Part US9113538B2 (en) | 2011-05-20 | 2013-09-27 | Structure electron beam inspection system for inspecting extreme ultraviolet mask and structure for discharging extreme ultraviolet mask |
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EP4052277A1 (en) * | 2019-10-28 | 2022-09-07 | ASML Netherlands B.V. | System for inspecting and grounding a mask in a charged particle system |
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